Image sensing apparatus

ABSTRACT

An image sensing apparatus has a light flux splitter disposed between a lens that focuses light flux of an object image on an image sensing surface and that image sensing surface and that branches the light flux of the object image out of an image sensing light path, a light receiving unit that receives the light flux of the object image branched by the light flux splitter and obtains a signal for focusing control of the lens, and a holding unit that holds the light flux splitter at either an effective position within the image sensing light path or at a retracted position outside the image sensing light path. The image sensing apparatus automatically holds the light flux splitter at either the effective position or the retracted position depending on image sensing conditions.

FIELD OF THE INVENTION

The present invention relates to an image sensing apparatus having alight flux splitter positioned between the lens and the image sensingsurface that separates the light flux of an object image out of theimage sensing light path, and a control method for such image sensingapparatus.

BACKGROUND OF THE INVENTION

Conventionally, a method of separating the light flux of an object imageand directing it to a photo-sensing element for the purpose of focusdetection has been proposed. For example, Japanese Laid-Open PatentApplication Publication No. 63-195630 relates to a camera equipped witha zoom lens, and discloses a technology in which the light flux is splitat an intermediate point along the light path of the zoom lens and focusdetection is conducted using this split light flux. In addition,Japanese Laid-Open Patent Application Publication No. 2003-140246discloses an invention relating to a digital single-lens reflex camerathat focuses a primary object image formed by an image forming opticalsystem onto a two-dimensional photo-sensing sensor such as a CCD sensoror a CMOS sensor, photoelectrically converts the optical image thusobtained, and obtains image output for that object.

In the foregoing proposals, the light flux of an object image is dividedby a splitter or other light flux splitter and separately incident onthe image sensor and the focus detection sensor, with detection of thestate of focus carried out on the focus detection sensor side and imagesensing carried out on the image sensor side.

In the conventional examples described above, the splitter or other suchlight flux splitter is provided within the light flux of an objectimage. However, using such a light flux splitter generally diminishesthe amount of light that reaches the image sensor. To counteract thiseffect, the light flux splitter may be retracted during image sensing sothat all the light strikes the image sensor, but retracting the lightflux splitter with every sensing of an image leads to shutter time lag.

SUMMARY OF THE INVENTION

The present invention has been made in light of the above-describedsituation, and has as its object to provide an image sensing apparatusthat eliminates shutter time lag during image sensing as the light fluxsplitter is retracted while capable of carrying out good image sensing,and a control method for such an image sensing apparatus.

According to the present invention, the foregoing object is attained byproviding an image sensing apparatus comprising:

a light flux splitter disposed between a lens that focuses light flux ofan object image on an image sensing surface and that image sensingsurface and that branches the light flux of the object image out of animage sensing light path;

a light receiving unit that receives the light flux of the object imagebranched by the light flux splitter and obtains a signal for focusingcontrol of the lens; and

a holding unit that holds the light flux splitter at either an effectiveposition within the image sensing light path or at a retracted positionoutside the image sensing light path,

wherein the image sensing apparatus automatically holds the light fluxsplitter at either the effective position or the retracted positiondepending on image sensing conditions.

In addition, according to the present invention, the foregoing object isalso attained by providing A control method for an image sensingapparatus having a light flux splitter disposed between a lens thatfocuses light flux of an object image on an image sensing surface andthat image sensing surface and that branches the light flux of an objectimage out of an image sensing light path, a light receiving unit thatreceivers the light flux of the object image branched by the light fluxsplitter and obtains a signal for focusing control of the lens; and aholding unit that holds the light flux splitter at either an effectiveposition within the image sensing light path or at a retracted positionoutside the image sensing light path, the control method comprising:

determining whether to carry out image sensing with the light fluxsplitter at the effective position or at the retracted positiondepending on image sensing conditions; and

retracting the light flux splitter to the retracted position prior toimage sensing if it is determined that image sensing is to be carriedout with the light flux splitter positioned at the retracted position.

Other objects, features and advantages of the present invention will beapparent from the following description when taken in conjunction withthe accompanying drawings, in which like reference characters designatethe same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a sectional view of the essential structure of a digitalcamera according to a first embodiment of the present invention;

FIG. 2 is a block diagram showing the electrical structure of thedigital camera shown in FIG. 1;

FIG. 3 is a structural diagram showing a lens barrel portion in a casein which a splitter is at an effective position in the digital camerashown in FIG. 1;

FIG. 4 is a structural diagram showing the lens barrel portion in a casein which the splitter is at a retracted position in the digital camerashown in FIG. 1;

FIG. 5 is a sectional view of the splitter shown in FIG. 2;

FIG. 6 is perspective view of the splitter shown in FIG. 2;

FIG. 7 is an exploded perspective view of the splitter shown in FIG. 2;

FIG. 8 is a diagram showing the optical characteristics of a lightsplitting surface of the splitter shown in FIG. 2;

FIG. 9 is a diagram showing an example of the optical characteristics ofan ordinary ND filter used in a digital camera;

FIG. 10 is a focus detection view field generated by an AF moduleaccording to the first embodiment of the present invention;

FIG. 11 is a plan view of a focus detection surface of an AF moduleaccording to the first embodiment of the present invention;

FIG. 12 is a sectional view of the pixel part of an image sensingelement according to the first embodiment of the present invention;

FIGS. 13A and 13B are plan views of a photoelectric conversion part ofone pixel of the image sensing element according to the first embodimentof the present invention;

FIG. 14 is a plan view showing a state in which pixels of the imagesensing element according to the first embodiment of the presentinvention are linked together and arranged in an array used for focusdetection;

FIG. 15 is an exploded perspective view showing a state in which pixelsof the image sensing element according to the first embodiment of thepresent invention are linked together and arranged in an array used forfocus detection;

FIG. 16 is a plan view showing openings 154A, 154B of a first wiringlayer 154 shown in FIG. 15;

FIG. 17 is a partial sectional view of a focus detection view field112-1 according to the first embodiment of the present invention;

FIG. 18 is a partial sectional view of the focus detection view field112-1 according to the first embodiment of the present invention;

FIG. 19 is a diagram showing a focus detection sensor output signalwaveform input to an AF control circuit 140 shown in FIG. 2;

FIG. 20 is a diagram showing a focus detection sensor output signalwaveform input to the AF control circuit 140 shown in FIG. 2;

FIG. 21 is a diagram illustrating a transit area of a focus detectionlight flux on an exit pupil of an image forming optical system 102 shownin FIG. 1;

FIG. 22 is a diagram illustrating an image sensing light flux accordingto the first embodiment of the present invention;

FIG. 23 is a sectional view of a splitter part drawn on a focusdetection light flux according to the first embodiment of the presentinvention;

FIG. 24 is a diagram showing unevenness in luminance of an image in thefirst embodiment of the present invention;

FIG. 25 is a diagram showing unevenness in luminance of an image in thefirst embodiment of the present invention;

FIGS. 26A and 26B are structural diagrams showing side and front views,respectively, of a case in which the splitter and its holding memberaccording to the first embodiment of the present invention are at theeffective position;

FIG. 27 shows a front view of a case in which the splitter and itsholding member according to the first embodiment of the presentinvention are at the retracted position;

FIG. 28 is a flow chart illustrating the processes performed by theimage sensing apparatus according to the splitter of the firstembodiment of the present invention;

FIG. 29 is a structural diagram showing a front view in a case in whichthe splitter and its holding member according to a second embodiment ofthe present invention are at the effective position;

FIG. 30 is a structural diagram showing a side view of the splitter andits holding member shown in FIG. 29;

FIG. 31 is a flow chart illustrating the processes performed by theimage sensing apparatus relating to the splitter in the secondembodiment of the present invention; and

FIG. 32 is a flow chart illustrating the processes performed by theimage sensing apparatus relating to the splitter in a third embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings. However, thedimensions, shapes and relative positions of the constituent parts shownin the embodiments should be changed as convenient depending on variousconditions and on the structure of the apparatus adapted to theinvention, and the invention is not limited to the embodiments describedherein.

First Embodiment

FIG. 1 shows a sectional view of a digital camera according to a firstembodiment of the present invention.

In FIG. 1, reference numeral 101 designates a digital camera, 102designates an image forming optical system for forming an image of anobject, 104 designates the optical axis of the image forming opticalsystem 102 and 105 designates a lens barrel that contains the imageforming optical system 102.

The above-described image forming optical system 102 can adjust theposition of the image forming position in the direction of the opticalaxis 104 by an energy source, not shown, and a drive mechanism, notshown. The focusing lens may be composed of a flexible transparentelastic member and a fluid lens so that it can also focus on an objectby varying the surface shape and changing the refracting power of thefocusing lens. The image forming optical system 102 may also be a singlefocus lens, a zoom lens, or a shift lens and the like. In addition, theimage forming optical system 102 may also be made so as to beinterchangeable with an image forming optical system equipped with avariety of characteristics (F-number, focal distance and so forth). Acomposite material consisting of acrylic resin uniformly coated withparticles of niobium oxide approximately 5 nm to 30 nm in size may beused as the material for the lens that comprises the image formingoptical system 102. In that case, the lens has a high refractive indexof approximately 1.8 yet is more resistant to shock than glass, andfurthermore, can be manufactured inexpensively by injection molding.

Reference numeral 103 designates a splitter that splits a light flux,110 designates the optical axis inside the splitter 103, 111 designatesa shutter release button, 108 designates a memory card that stores imagedata, 109 designates an optical viewfinder eyepiece, 106 designates animage sensing element such as a two-dimensional CCD and CMOSphotoreceptive sensor, 112 designates a focus detection sensor (an AFsensor) included in an AF module and 113 designates an optical low-passfilter. During acquisition and image sensing of an image displayed on adisplay device 107 that is described later, a light flux passing throughthe splitter 103 and the optical low-pass filter 113 is projected ontothe image sensing element 106. Reference numeral 114 designates a planeparallel plate optical member for correcting the light path length, andfunctions to correct variations in the light path length due toretraction of the splitter 103 from within the light flux (along theoptical axis 104).

Reference numeral 107 designates the aforementioned display device,mounted on a rear surface of the camera. Images of objects taken by theimage sensing element 106 are displayed on this display device 107. Theuser can determine the composition of image sensing by observing thedisplay device 107 directly in preparation for image sensing. Thedisplay device 107 is composed of an organic EL (ectroluminescence)spatial modulation element, a liquid crystal spatial modulation element,a spatial modulation element that utilizes the electrophoresis ofparticles or the like, and thus consumes little power, is compact, thin,and conveniently easy to use.

The image sensing element 106 performs image output for the displaydevice 107 using interlaced scanning and high-definition scanning ofreading out all pixels during image sensing.

FIG. 2 is a block diagram showing the electrical structure of thedigital camera 101.

The digital camera 101 comprises an image sensing system, an imageprocessing system, a recording and playback system and a control system.The image sensing system includes the image forming optical system 102and the image sensing element 106. The image processing system includesan A/D converter 130, an RGB image processing circuit 131 and a YCprocessing circuit 132. The recording and playback system includes arecording processing circuit 133 and a playback processing circuit 134.The control system includes a camera system control circuit 135, aninformation display circuit 142, an operating control detection circuit136 and an image sensing element drive circuit 137. Reference numeral138 designates a connection terminal connected to an external computeror the like and standardized to transmit and receive data. Theseelectrical circuits are, for example, driven by a miniature fuel cell,not shown. It should be noted that the type of power source is notlimited to a fuel cell, and alternatively any ordinary power source canbe used.

The image sensing system is an optical processing system that focuseslight from an object onto an image sensing surface of the image sensingelement 106 through the image forming optical system 102. It controls adiaphragm and a mechanical shutter, not shown, of the image formingoptical system 102 so that the image sensing element 106 is exposed toan appropriate amount of light from the object. A photo-sensing elementhaving, for example, a total of 8 million pixels arranged in arectangular array 3264 pixels in the long direction and 2448 pixels inthe short direction may be used for the image sensing element 106. Thepixels of the photo-sensing element are arranged, for example, in aso-called Bayer arrangement, consisting of red (R), green (G) and blue(B) color filters arranged alternately, with four pixels forming a set.In the Bayer arrangement, overall image performance is improved byproviding more of the pixels of G to which an observer is more sensitivethan the R or B pixels. In general, in image processing using this typeof image sensing element, most of the luminance signal is generated fromthe G whereas the color signal is generated from the R, G, and B.

The image signal read out from the image sensing element 106 is suppliedto the image processing system through the A/D converter 130. The A/Dconverter 130 is a signal conversion circuit that converts the signalsfrom the pixels that are exposed into, for example, 12-bit digitalsignals depending on the amplitude of the signals and outputs theresulting 12-bit digital signals, with succeeding image signalprocessing executed as digital processing.

The image processing system is a signal processing circuit that obtainsimage signals of a desired format from the R, G, B digital signals, andcoverts the R, G, B color signals into a luminance signal Y and YCsignals expressed as color difference signals (R-Y) and (B-Y). The RGBimage processing circuit 131 is a signal processing circuit thatprocesses the image signals of the pixels received from the imagesensing element 106 through the A/D converter 130, and has a whitebalance circuit, a gamma correction circuit and an interpolationcalculation circuit that boosts image resolution by interpolationcomputation.

The YC processing circuit 132 is a signal processing circuit thatgenerates a luminance signal Y and color difference signals (R-Y) and(B-Y). The YC processing circuit 132 comprises a high-luminance signalgenerating circuit that generates a high-luminance signal YH, alow-luminance signal generating circuit that generates a low-luminancesignal YL, and a color difference signal generating circuit thatgenerates color difference signals (R-Y) and (B-Y). The luminance signalY is formed by combining the high-luminance signal YH and thelow-luminance signal YL.

The recording and playback system is a processing system that outputsimage signals to the memory and outputs image signals to the displaydevice 107. The recording processing circuit 133 writes image signalsinto and reads image signals out from the memory, and the playbackprocessing circuit 134 plays back image signals read from the memory andoutputs the image signals to the display device 107. In addition, therecording processing circuit 133 has a built-in compression/expansioncircuit that compresses the YC signals that express still images andmoving images using a predetermined compression format and expands thecompressed data when it is read out. The compression/expansion circuitincludes a frame memory and the like for signal processing, and the YCsignals from the image processing system are accumulated in the framememory one image at a time, each of which is read out andcompression-encoded at each plurality of blocks. The compressionencoding is carried out, for example, by two-dimensional orthogonaltransform, normalization and Huffman encoding. The playback processingcircuit 134 is a circuit that matrix-transforms the luminance signal Yand the color difference signals (R-Y) and (B-Y), and converts theminto, for example, an RGB signal. The signals converted by the playbackprocessing circuit 134 are output to the display device 107, where theyare displayed and reproduced as visible images.

The control system includes the operating control detection circuit 136that detects operations of the shutter release button 111 and the like,and the camera system control circuit 135 that controls the parts of thecamera 101 in response to the detected signals and generates and outputstiming signals during image sensing and the like. The control systemfurther includes the image sensing element drive circuit 137, whichgenerates drive signals that drive the image sensing element 106, andthe information display circuit 142, which controls the informationdisplay device inside the optical viewfinder and the information displaydevice on the outside of the camera, under the control of the camerasystem control circuit 135. In addition, the control system controls theimage sensing system, the image processing system and the recording andplayback system in response to external operations, so as to, forexample, detect depression of the shutter release button 111 and controlthe driving of the image sensing element 106, the operation of the RGBimage processing circuit 131 and the compression processing of therecording processing circuit 133, and further, controls the state ofeach segment of the information display device that displays informationin the optical viewfinder and the like carried out by the informationdisplay device 142.

An AF control circuit 140 and a lens system control circuit 141 arefurther connected to the camera system control circuit 135. The AFcontrol circuit 140 and the lens system control circuit 141 exchangedata needed for individual processes performed through the camera systemcontrol circuit 135. The AF control circuit 140 obtains the signaloutput of a focus detection field of view of the focus detection sensor112 set so as to correspond to a predetermined position on the imagesensing screen and generates a focus detection signal, and detects thestate of image formation of the image forming optical system 102. Astate of defocus, if detected, is converted into a drive amount for thefocusing lens that is one element of the image forming optical system102 and relayed through the camera system control circuit 135 to thelens system control circuit 141. In addition, with respect to a movingobject, the AF control circuit 140 considers the time lag from the timethe shutter release button 111 is pressed to the time at which actualimage sensing control commences, predicts the appropriate lens positionand orders the requisite focusing lens drive amount. When it isdetermined that the luminance of the object is low and adequate focusdetection accuracy cannot be obtained, the AF control circuit 140illuminates the object with an flash device, not shown, or a white LEDor fluorescent light, not shown, to compensate for the inadequateluminance.

When the lens system control circuit 141 receives the instructionindicating the drive amount of the focusing lens, it moves the focusinglens in the image forming optical system 102 along the optical axis 104using a drive mechanism, not shown, and focuses on the object. When as aresult of a sequence of focus adjustment operations the AF controlcircuit 140 detects that the image is in focus, this information istransmitted to the camera system control circuit 135. At this time, whenthe shutter release button 111 is pressed to a second stage and thesplitter 103 should be retracted from the light path, the splitter 103and the plane parallel plate 114 are exchanged by a mechanism that isdescribed later. Then, a high-definition image is formed by the lightflux that passes through the optical low-pass filter 113, accomplishingimage sensing control via the image sensing system, the image processingsystem, and the recording and playback system as described above. Atthis point, the plane parallel plate 114 is inserted at the positionwhere the splitter 103 was so that fluctuations in the focus of theimage forming optical system 102 do not occur, and thus there is no needto correct the focus. Therefore, it is possible to provide a shortrelease-time lag without adversely affecting high-speed focus detection.

FIG. 3 is a sectional view of the lens barrel 105 portion of the digitalcamera 101 preparatory to image sensing, FIG. 4 is a sectional view ofan image sensing state, FIG. 5 is a sectional view of the splitter 103,FIG. 6 is perspective view of the splitter 103 and FIG. 7 is an explodedperspective view of the splitter 103. A detailed description is nowgiven of the splitter 103 and its peripheral units using the foregoingdrawings.

The splitter 103 is positioned between the rear end of the lens group ofwhich the image forming optical system 102 is comprised and the imagesensing element 106. Reference numeral 102 a designates the focusinglens, which adjusts the focus by moving along the optical axis 104. Theimage sensing element 106 is fixed in position with respect to a fixedfloor panel, not shown, of the lens barrel 105. In addition, the opticallength of the splitter 103 in the visible wavelength range is made tomatch an optical length determined by the thickness of the planeparallel plate 114. Thus, when the splitter 103 shown in FIG. 3 isretracted and the plane parallel plate 114 is inserted in place of thesplitter 103 as shown in FIG. 4, the state of focus on the image sensingelement 106 of the image forming optical system 102 does not change.

The general image sensing sequence is as follows: When it is detectedthat the shutter release button 111 is depressed to the first stage, theimage sensing element 106 is driven and the object image formed with thelight flux that passes through the splitter 103 is repeatedly sensed andthe object image is displayed in real time on the display device 107. Inaddition, focus detection is carried out using the focus detectionsensor 112 with the light flux of the visible wavelength range split bythe splitter 103. If the extent of defocus meets or exceeds apredetermined amount, the extent to which the focusing lens 102 a is tobe driven is calculated and the focusing lens 102 is moved along theoptical axis 104 by that amount and focusing control is carried out.After focusing control is completed, focus detection is carried outusing the focus detection sensor 112 again. Once it is confirmed thatthe amount of defocus is within a predetermined range, focus display bysound and light is provided.

When it is detected that the shutter release button 111 is depressed tothe second stage and the splitter 103 should be retracted from the lightpath for example during exposure, the splitter 103 is retracted from thelight path of the image forming optical system 102 by a mechanism thatis described later and the plane parallel plate 114 is inserted in itsplace (see FIG. 4). The image sensing element 106 is driven and imagesensing is carried out in the high-definition mode. Then, after imagesensing is completed, the plane parallel plate 114 is retracted from thelight path of the image forming optical system 102 and the splitter 103is returned to its original position (see FIG. 3). Image data pertainingto the sensed object image is then written to the memory.

Next, a detailed description is given of the light splitting function.As shown in FIGS. 5-7, the splitter 103 comprises two prisms, 103-1 and103-2, adhered together at a light splitting surface 103 a. The lightentry surface of the splitter 103 is formed by a surface 103-1 b of theprism 103-1 and a surface 103-2 b of the prism 103-2, and the exitsurface for light advancing straight ahead is formed by a surface 103-1d of the prism 103-1 and a surface 103-2 d of the prism 103-2. There isno gap between surface 103-1 b of prism 103-1 and surface 103-2 b ofprism 103-2, and there is no gap between surface 103-1 d of prism 103-1and surface 103-2 d of prism 103-2. In addition, the surfaces 103-1 band 103-1 d of prism 103-1 and the surfaces 103-2 b and 103-2 d of prism103-2 are parallel.

The surface 103-b 1 of the prism 103-1 and the light splitting surface103 a, and the surface 103-2 d of the prism 103-2 and the lightsplitting surface 103 a, have different angles of inclination. Surface103-1 b and light splitting surface 103 a, and surface 103-2 d and lightsplitting surface 103 a, respectively, intersect.

The light splitting surface 103 a of the splitter 103 is formed byforming a dielectric multilayer film on a surface 103-2 a of the prism103-2 and affixing it to a surface 103-1 a of the prism 103-1 using anindex-matching optical adhesive to obtain the desired opticalcharacteristics. The optical characteristics of the light splittingsurface 103 a are as shown in FIG. 8. The spectral transmittancecharacteristics of wavelengths from 400 nm to 1000 nm form a concave-upcurve with its minimum value near 500 nm, whereas the spectralreflectance characteristics form a concave-down curve with its maximumvalue near 500 nm. In other words, the light splitting surface 103 areflects a portion of the entering light of a predetermined wavelengthrange and permits the rest to pass through. As the distinctive featureof the dielectric multilayer film, absorption can be made small enoughso that it can be substantially ignored, and thus at the light splittingsurface 103 a the entering light is divided in the directions toward theimage sensing element 106 and toward the focus detection sensor 112.

In a visible spectrum range from 450 nm to 650 nm, it can be seen thatthe spectral transmittance is constant at about 45 percent. In a colorcamera, the photographic sensitivity range of the image sensing element106 is made to match the visible light range, and thus the spectralreflectance in the sensitive wavelength range of the image sensingelement 106 can be said to be flat.

Of the light fluxes striking the splitter 103 from the light entrysurface formed by surface 103-1 b of prism 103-1 and surface 103-2 b ofprism 103-2, the light flux reflected by the light splitting surface 103a is totally reflected at surface 103-2 b and exits from surface 103-2c. The focus detection sensor 112 is disposed at a position opposing tosurface 103-2 c and the light flux from the splitter 103 strikes thelight splitting surface 103 a, by which the focus detection functionoperates.

The spectral characteristics of the light flux split by the splitter 103as described above are substantially the same as those of the light thattravels straight ahead, and it is this light flux that triggers thefocus detection function. The spectral reflectance here is approximately55 percent, making high-accuracy focus detection due to an adequateamount of light possible. It should be noted that, in order to match thespectral sensitivity of the focus detection sensor 112 exactly to theimage sensing element 106, it is better still to add an infrared raycut-out function to the entry surface protective glass of the focusdetection sensor 112.

An ND (Neutral Density) filter is formed on surface 103-1 b of prism103-1 and surface 103-2 b of prism 103-2. The ND filter is a type oflight-absorbing film, in which vapor coating of chromel or the like isused to obtain flat transmittance characteristics over a very wide rangeof wavelengths. Chromel is a metal alloy composed chiefly of nickel, ina composition ratio of Cr: 7.0-10.5 percent, Mn: 1.5 percent or less,and Si: 1.0 percent or less.

FIG. 9 shows an example of the optical characteristics of an ND filterformed using chromel vapor coating. In the visible spectrum range from450 nm to 650 nm, the spectral transmittance is constant atapproximately 45 percent, and with such high absorption the spectralreflectance in this range is approximately 15 percent.

Next, a description is given of the focus detection sensor 112. FIG. 10shows a focus detection view field of the focus detection sensor 112.

In FIG. 10, reference numeral 120 designates a viewfinder view field inwhich the image sensing range is made to coincide with the observationrange, with reference numerals from 121-1 to 121-9 delineating the focusdetection view field. Setting the focus detection view field near thecenter of the image sensing range makes the camera easy to use. Thefocus detection view field comprised of columns of pixels in thevertical direction is sensitive to vertical luminance distribution, thusenabling, for example, focus detection of horizontal lines. At the sametime, the focus detection view field comprised of rows of pixels in thehorizontal direction is sensitive to the horizontal luminancedistribution, thus enabling, for example, focus detection of verticallines, The actual focus detection sensor 112 is configured as shown inFIG. 11. FIG. 11 is a plan view of the focus detection sensor 112, withreference numerals from 112-1 to 112-9 designating pixel arrays formingfocus detector views field 121-1 to 121-9.

FIG. 12 is a sectional view of the pixel part of a focus detection viewfield (for example 121-1) of the image sensing element 112. FIG. 13A isa plan view of a photoelectric conversion part of one pixel of the imagesensing element 112. FIG. 13B shows a microlens disposed atop thephotoelectric conversion part shown in FIG. 13A.

Light, in FIG. 12, strikes the focus detection sensor 112 from the topof the diagram, and in FIGS. 13A and 13B, strikes the focus detectionsensor 112 from in front of the plane formed by the sheet of paper onwhich the diagram is drawn. The focus detection sensor 112 is a CMOSsensor having a one-chip-type microlens. By the operation of themicrolens the focus detection light flux F-number can be set.

In FIG. 12, the reference numeral 151 designates a silicon substrate,152A and 152B designate photoelectric conversion parts of embeddedphotodiodes, 154 designates a light-blocking first wiring layer made ofaluminum or copper, and 155 designates a second wiring layer made ofaluminum or copper. In addition, reference numeral 156 designates apassivation film and an interlayer insulation film composed of siliconoxide film, hydrophobic porous silica, silicon oxynitride film orsilicon nitride film, and 158 designates a microlens. In addition,reference numeral 157 designates a flattened layer for setting thedistance from the second wiring layer 155 to the microlens 158accurately. The first wiring layer 154 and the second wiring layer 155are metallic films with dispersed openings provided therein, and do notpermit visible light to pass through areas other than these openings.The first wiring layer 154 and the second wiring layer 155 have both theelectrical function of triggering the focus detection sensor 112 and theoptical function of controlling the angular characteristics of thereceived light flux. The flattened layer 157 is formed by suchtechniques as spin coating a thermosetting resin or an ultravioletsetting resin and then curing the resin or by adhesion of a resin filmor the like.

The photoelectric conversion parts 152A, 152B are zigzag-shaped as shownin FIG. 13A, to the ends of which are connected circuit units 159A,159B. The circuit units 159A, 159B have a transfer MOS transistor thatfunctions as a transfer switch and a reset MOS transistor that suppliesa reset bias voltage, and further, have a source-follower amp MOStransistor, a selection MOS transistor for selectively outputtingsignals from the source follower amp MOS transistor, and the like. Fivemicrolenses 158 connected in a zigzag pattern are mounted on thephotoelectric conversion part 152 (152A, 152B) as shown in FIG. 13B.

The microlens 158 is formed using resin, SiO2, TiO2, Si3N4 or the likeand is used not only simply to concentrate light but also to formimages, and consequently is an axially symmetrical spherical lens or anaxially symmetrical non-spherical lens. Accordingly, because themicrolens 158 is shaped so as to have an axis of symmetry 160 (see FIG.12) it appears circular when viewed from above. However, by mountingmultiple microlenses on each individual pixel, the photo-sensing surfacearea of each pixel can be increased even as the pixel pitch isdecreased. Therefore, adequate focus detection output can be obtainedeven for low-luminance objects. Moreover, a shape like that, forexample, of a Quonset hut or the like, which lacks axial symmetry, doesnot have an image forming effect as does a lens, and thus is notsuitable for the focus detection sensor 112. It should be noted that, inorder to reduce surface reflection of the light, a low-refractive indexthin film or a minute structure smaller than the wavelength of visiblelight (a so-called sub-wavelength structure) may be formed on thesurface of the microlens 158.

The light flux emitted from the splitter 103 first strikes the microlens158 of the focus detection sensor 112, and the portion that passesthrough the opening 155A provided in the second wiring layer 155 and theopening 154A provided in the first wiring layer 154 then strikes thephotoelectric conversion part 152A. The portion that passes through theopening 155A provided in the second wiring layer and the opening 154Bprovided in the first wiring layer 154 then strikes the photoelectricconversion part 152B. Each portion is then converted into an electricalsignal. The first wiring layer 154 and the second wiring layer 155 arealso used as the light-blocking layer for forming the openings, and thusthere is no need to provide a special light-blocking layer for theopenings, thereby allowing the structure of the focus detection sensor112 to be simplified.

FIG. 14 and FIG. 15 show plan and perspective views, respectively, ofthe state of the pixel array in which the pixels shown in FIGS. 13A and13B are linked and used for focus detection.

In FIG. 14, the microlenses 158 at both ends has been omitted so as toreveal the photoelectric conversion part in order to facilitate anunderstanding of the relation between the photoelectric conversion part152 (152A, 152B) and the microlens 158. Moreover, in FIG. 15, of theconstituent elements, the photoelectric conversion part 152, the firstwiring layer 154, the second wiring layer 155 and the microlens 158 areextracted and shown in the form that they are exploded vertically. Inorder to delineate the boundaries of each individual pixel, the zigzagshape of the photoelectric conversion part is projected onto the firstwiring layer and the second wiring layer and indicated by the brokenline.

In FIG. 14, the five shaded microlens 158 a correspond to a singlepixel, and multiple such pixels are linked horizontally to form thepixel arrays 112-1 to 112-9 shown in FIG. 11. The microlenses aligned ina zigzag just cover the space between them and the microlenses ofadjacent pixels, and thus the microlenses are spread tightly togetheratop the pixel array. Therefore, the light fluxes that do not strike themicrolens and are not used are few enough that they can be virtuallyignored.

In addition, when noting the direction of arrangement, the zigzagalignment allows the pixel frequency response around the Nyquistfrequency to be decreased. As a result, aliasing distortion does noteasily occur even with the image sensing of an object image including ahigh spatial frequency component equal to or greater than the Nyquistfrequency, enabling high-accuracy phase difference detection betweenoutput signal waveforms of the focus detection sensor 112 that isdescribed later to be carried out. Furthermore, around the pixel arrayare formed microlenses 158 b, indicated by hatching, which are notdisposed atop the photoelectric conversion part and which do notcontribute to photoelectric conversion. These microlenses 158 arepresent because, for production reasons, spreading the microlenses asuniformly as possible permits precision manufacture of the microlenses158.

The first wiring layer 154 shown in FIG. 15 has multiple diamond-shapedopenings 154A, 154B. As shown in the plan view shown in FIG. 16, onepair of the openings 154A, 154B are provided for each microlens 158,positioned near the focus of the microlens 158 in the direction ofdepth. With such a structure, the openings 154A, 154B are back-projectedonto the exit pupil of the image forming optical system 102 by themicrolens 158, and thus it is possible to determine the photo-receivingangle characteristics of the light flux taken in by the pixel by theshape of the openings 154A, 154B. The opening 155A provided in thesecond wiring layer 155 is an aperture for preventing light fromentering openings other than openings 154A, 154B in the first wiringlayer 154. As a result, only those light fluxes which can pass throughthe openings 154A, 154B strike the respective photoelectric conversionpart 152A, 152B. Here, in order to prevent non-uniformity in the outputsignal output-from the pixel arrays of the focus detection sensor 112,the shapes of the openings 154A, 154B for the pixel array that forms asingle focus detection view field are constant.

FIG. 17 and FIG. 18 are partial sectional views of the focus detectionview field 121-1 (pixel array 112-1) shown in FIG. 10. The microlenses158 back-project the openings 154A, 154B in the first wiring layer 154onto the exit pupils of the image forming optical system 102, and thus,as shown in FIG. 17, a light flux 132A is permitted to pass through theopening 154A. This arrangement is the equivalent of the light flux 132Aexiting from the back-projected image of the opening 154A in the firstwiring layer 154.

Similarly, as shown in FIG. 18, a light flux 132B is permitted to passthrough the opening 154B. This is equivalent to the light flux 132Bexiting from the back-projected image of the opening 154B in the firstwiring layer 154. Therefore, light rays striking the focus detectionsensor 112 from anything other than the back-projected images of theopenings 154A, 154B are blocked by the first wiring layer 154 or thesecond wiring layer 155 and cannot reach the photoelectric conversionparts 152A, 152B, and are not photoelectrically converted. For the pixelarray that forms a single focus detection view field, the followingstate can be observed between the output signal waveform obtained byarranging the output signals from the photoelectric conversion part 152Aand the output signal waveform obtained by arranging the output signalsfrom the photoelectric conversion part 152B: Specifically, depending onthe state of focus of the object image formed by the image formingoptical system 102 on the focus detection view field, a relative lateralshift is observed. This shift arises because the area through which thelight flux passes on the exit pupil of the image forming optical systemdiffers between the output signal waveform obtained by arranging theoutput signals from the photoelectric conversion part 152A and theoutput signal waveform obtained by arranging the output signals from thephotoelectric conversion part 152B. Between front-focused andrear-focused the output signal waveform shift direction reverses itself,and using a technique such as correlation calculation or the like todetect this phase difference (that is, this shift amount) as well as itsdirection is the basic principle of focus detection.

FIG. 19 and FIG. 20 show output signal waveforms of the focus detectionsensor 112 input to the AF control circuit 140, in which the horizontalaxis represents pixel alignment and the vertical axis represents outputvalues, respectively.

FIG. 19 shows the output signal waveforms in a state in which the objectimage is out of focus and FIG. 20 shows the output signal waveforms in astate in which the object image is in focus. Thus, first, by judging theidentity (similarity) of a set of signals, focus detection can becarried out. Furthermore, by using a well-known technique employingcorrelation calculation, for example, the technique disclosed inJapanese Laid-Open Patent Application Publication No. 05-088445 todetect a phase difference, the amount of defocus can be obtained.Converting the defocus amount so obtained into the amount the focusinglens 102 a of the image forming optical system 102 should be drivenmakes automatic focusing control possible. Since the amount the focusinglens 102 a should be driven is known in advance, the driving of the lensto the focus position is normally accomplished in essentially one driveoperation, thus providing high-speed focusing control.

Here, a description is given of the focus detection light flux. Thefocus detection sensor 112 varies the F-number of the focus detectionlight flux with each focus detection view field by controlling thephoto-receiving angle characteristics with each focus detection viewfield. The size of the area through which the light flux passes on theexit pupil of the image forming optical system is large in the centerfocus detection view field 121-1 and small in the periphery focusdetection view field 121-4.

FIG. 21 illustrates the area through which the focus detection lightflux passes on the exit pupil of the image forming optical system 102. Apupil area 141 shows a vignetting of the aperture of the image formingoptical system 102 when seen from the edge of the focus detection viewfield 121-1, and a pupil area 145 shows a vignetting of the aperture ofthe image forming optical system 102 when seen from the edge of thefocus detection view fields 121-4, 121-5, 121-6 and 121-7. By contrast,pass-through areas 143A, 143B of the focus detection light flux of thefocus detection view field 121-1 are located inside the pupil area 141,and pass-through areas 144A, 144B of the focus detection light flux ofthe focus detection view field 121-4 are located inside the pupil area145.

The broader the pass-through area of the focus detection light flux thegreater the amount of light striking the photo-sensor, and focusdetection of even low-luminance objects can be carried out accurately.In terms of efficient utilization of the light from the object, in thisstructure the actual area through which the focus detection view fieldflux passes is also large in the focus detection view field 112-1 of thescreen center in which the pupil area as a characteristic of the imageforming optical system 102 is large. At the same time, in the focusdetection view field 121-4 of the screen periphery, in which the pupilarea as a characteristic of the image forming optical system 102 isnarrow and often vignetted, the actual area through which the focusdetection light flux passes is also narrow. Therefore, it can beunderstood that the two requirements concerning the amount of light atthe center of the screen and the positioning of the focus detection viewfield at the periphery of the screen are neatly satisfied and the lightfrom the object is used very efficiently.

Next, a description is given of the area through which the focusdetection light flux passes on the splitter 103. FIG. 22 shows asectional view of the splitter 103 and its vicinity depicting the focusdetection light flux.

In FIG. 22, reference numeral 170 designates a focus detection lightflux heading toward the focus detection view field 121-3 of the focusdetection sensor 112, 171 designates a focus detection light fluxheading toward the focus detection view field 121-1 and 172 designates afocus detection light flux heading toward the focus detection view field121-2. After the focus detection light fluxes 170, 171, 172 arereflected by the light splitting surface 103 a, at surface 103-2 b thefocus detection light fluxes 170, 171, 172 are fully reflected by thedifference in refractive index between the air and the prism 103-2 andexited from the surface 103-2 c. In the cross-section shown in FIG. 22,the focus detection light fluxes 170 and 172 pass through the outermostareas of all the focus detection light fluxes, and thus it is sufficientto note the focus detection light fluxes 170 and 172 in deciding thesize of the effective ranges of the surfaces.

The splitter 103 is a part of the image forming optical system 102, andtherefore making the splitter 103 construction as thin as possiblefacilitates making the entire image forming optical system 102 compact.Particularly in a case in which the image forming optical system 102 isretracted into the body of the camera, the longer the space betweenoptical surfaces of the image forming optical system 102 the shorter thelength when stored. In order to make the thickness T of the splitter 103as small as possible, the length L of the light splitting surface 103 aand the depth D of the surface 103-2 c are to be set to values by addingmanufacturing tolerance to the smallest value that permits the focusdetection light fluxes to pass.

By setting the light splitting surface 103 a small so that only lightflux in the area of the focus detection view field enters the lightsplitting surface 103 a, light flux outside the focus detection viewfield does not strike the light splitting surface 103 a.

FIG. 23 illustrates an image sensing light flux. In FIG. 23, referencenumeral 173 designates an image sensing light flux striking the upperarea of the image sensing element 106, 174 designates an image sensinglight flux striking the central area of the image sensing element 106,and 175 designates an image sensing light flux striking the lower areaof the image sensing element 106. The image sensing light flux 174passes through the light splitting surface 103 a, and thus the light onthe exit pupil side of the splitter 103 acquires an intensitydistribution that is the product of the spectral transmittancecharacteristics at the light splitting surface 103 a multiplied by thespectral intensity characteristics of the object.

The image sensing light fluxes 170 and 172 pass through, respectively,surface 103-1 b of prism 103-1 and surface 103-2 d of prism 103-2, onwhich surfaces are formed the ND filter. Consequently, the light fluxexited from the splitter 103 has an intensity distribution that is theproduct of the spectral transmittance characteristics of the ND filterdescribed above using FIG. 9 multiplied by the spectral intensitycharacteristics of the object. In the visible wavelength range there isvirtually no difference between the spectral transmittancecharacteristics of the light splitting surface 103 a, surface 103-1 band surface 103-2 b, and therefore an image 180 of uniform brightness asshown in FIG. 24 is obtained when image sensing an optical image ofuniform luminance surface using the image sensing element 106. With nospecial luminance unevenness arising as a result, the upshot is imagesensing results that are not in any way different from ordinary images.If no ND filter were formed on surface 103-1 b of prism 103-1 and onsurface 103-2 d of prism 103-2, and permittivity is almost 100 percent.In that case, the image of the object sensed by the image sensingelement 106 would be an image 184 shown in FIG. 25, with a central darkarea 181 sandwiched top and bottom by bright areas 182 and 183. Thus,the effect of adjusting the permittivity using an ND filter can be saidto be very large.

FIG. 26A and FIG. 26B are sectional and front views, respectively, of acase in which an AF module containing the splitter 103 which is a lightflux splitting means and the focus detection sensor 112 is disposed inthe lens barrel 105.

In FIGS. 26A and 26B, an arm 201 that holds the splitter 103 isrotatably supported with respect to a fixed part of the lens barrel 105by a shaft 205 about which the arm 201 rotates. The rear surface of thesplitter 103 of the arm 201 is hollowed out, and the image sensing lightflux passes through the splitter 103 from the object image and the imagesensing lens and an image is formed on the image sensing element 106. Adrive coil 202 is fixed on the arm 201. When an electric current isapplied to the drive coil 202, a primary magnet 203 and a secondarymagnet 204 fixed on the lens barrel 105 side causes the arm 201 torevolve about the shaft 205. The arm 201, the coil 202, the primarymagnet 203, the secondary magnet 204 and the shaft 205 together compriseholding means for the light splitting means including the splitter 103.

Stoppers 206 a, 206 b are positioning pins for when the arm 201 comes tothe position shown in FIG. 26B, and by pressing the arm 201 against thestoppers 206 a, 206 b by an impelling force of the drive coil 202 thepositioning accuracy of the arm 201 is increased. In this position (theeffective position), the splitter 103 directs the image sensing lightflux to both the focus detection sensor 112 and the image sensingelement 106. When the arm 201 is in the position shown in FIG. 26B, ascan be understood from the side view shown in FIG. 23 the focusdetection sensor 112 is disposed opposite an end surface of the arm 201.

A description is now given of the primary magnet 203 and the secondarymagnet 204. FIG. 27 shows the arm 201 in a state of retraction from thelight path (that is, the retracted position), in which the primarymagnet 203 is magnetized in the direction of its thickness so that theNorth magnetic pole is formed in the direction projecting from thedrawing, and the secondary magnet is magnetized in the direction of itsthickness so that the North magnetic pole is formed in he directionsinking to the drawing.

When an electric current is applied to the drive coil 202, an electriccurrent flows through the drive coil 202 in directions indicated byarrows 202 e, 202 f, 202 g and 202 h. At this time, the direction of theelectric current in coil part 202 c (indicated by arrow 202 e) and thedirection of the magnetic flux of the primary magnet 203 subjects thecoil part 202 c to a force in a direction indicated by arrow 202 j withrespect to the primary magnet 203. In addition, the direction of theelectric current in coil part 202 d (indicated by arrow 202 g) is thereverse of the direction of the electric current indicated by arrow 202e, but because the direction of the magnetic flux of the secondarymagnet 204 is the reverse of the direction of magnetic flux of theprimary magnet 203 the coil part 202 d is subjected to the force exertedin the direction indicated by arrow 202 j with respect to the secondarymagnet 204. As a result, the arm 201 rotates counterclockwise about theshaft 205. At this point in time there is a slight chatter between thearm 201 and the shaft 205, which can result in drive accuracydeterioration. However, in FIG. 27, a combination of the direction ofthe electric current in a coil part 202 b (indicated by arrow 202 f) andthe direction of the magnetic flux of the primary magnet 203 subjectsthe arm 201 to an impelling force in the direction indicated by arrow202 i as well, which serves the function of reducing the chatter betweenthe arm 201 and the shaft 205. Thus, as described above, the splitter103 moves from the retracted position shown in FIG. 27 to the effectiveposition shown in FIGS. 26A and 26B with little chatter.

If electric current continues to be applied to the drive coil 202 evenafter the splitter 103 reaches the effective position shown in FIGS. 26Aand 26B, then the arm 201 is subjected to force in the directionindicated by arrow 202 j but is restricted by the stoppers 206 a, 206 band thus stops accurately at that position. In addition, the coil part202 b also is positioned inside the primary magnet 203, and thus the arm201 is also subjected to the force exerted in the direction indicated byarrow 202 i, which suppresses (by pressing aside) the chatter betweenthe shaft 205 and the arm 201. Furthermore, if the splitter 103 is atthe effective position, a portion of the coil part 202 d is positionedinside the primary magnet 203, and as a result the entire drive coil 202is subjected to a force in a normal direction of the drawing withrespect to the primary magnet 203, which in turn presses aside chatterin this direction as well so as to enable high-accuracy positioning.

When one wishes to return the splitter 103 to the retracted position, anelectric current in the reverse direction is applied to the drive coil202, by which the relative positions of the coil part 202 c and theprimary magnet 203, as well as the relative positions of a portion ofthe coil part 202 d and the secondary magnet 204, subject the arm 201 tothe force exerted in the direction opposite to arrow 202 j (the arm 201is also subjected to a force in the direction opposite the directionindicated by arrow 202 i). As a result, the arm 201 starts to rotateclockwise about the shaft 205 and the splitter 103 returns to theretracted position.

FIG. 28 is a flow chart illustrating the operation of the mechanismshown in FIGS. 26A, 26B and 27 through an image sensing sequence of acamera. This sequence of operations starts when the camera power isturned on and ends when the power is turned off. It should be notedthat, to avoid complication, descriptions of the operations of elementsnot directly related to the present invention and the detailed operationof each step (for example, confirmation after an operation or a standbyoperation with a timer) are omitted.

In step #1001, the image sensing element 106 is driven, object imageinformation is collected, a variety of processes are carried out on theobject image information with the RGB image processing circuit 131 andthe YC processing circuit 132, and the processed object imageinformation is output to the display device 107 so that the object imagecan be checked on the display device 107. In addition, during thisseries of processes the brightness of the object image is obtained, anddepending on that brightness, the diaphragm inside the lens barrel 105is adjusted and signals output from the image sensing element 106 areboosted so as to enable an object image of appropriate brightness to bedisplayed on the display device 107. Furthermore, this brightnessinformation is used in step #1008 to determine the necessity ofretracting the splitter 103.

Next, in step #1002, the cycling of step #1001 continues in a standbymode until the shutter release button 111 is pressed halfway(hereinafter described as S1). When pressed halfway (S1=ON), processingproceeds to step #1003. Then, in step #1003, charge corresponding to alight flux striking the focus detection sensor 112 through the splitter103 is accumulated and detection of the defocus amount (detection of thefocus state) is carried out. Thus, the splitter 103 normally ispositioned within the optical path of the image sensing lens (theeffective position shown in FIGS. 26A and 26B).

Next, in step #1004, in accordance with the focus detection results,part or all of the image forming optical system 102 is driven and theobject image is focused on the surface of the image sensing element 106.Then, in the next step #1005, charge corresponding to the light fluxstriking the focus detection sensor 112 is again accumulated and thedefocus amount is detected to confirm that the image is in focus.Although omitted from this sequence, if it is determined here that thefocus is inadequate, then, based on that result, the image formingoptical system 102 is again driven to correct the focus and the focusconfirmation operation is repeated. If after multiple iterations of theoperations described above the image is still out of focus, then amessage indicating that the camera cannot focus is displayed, focusingoperation is stopped and processing proceeds to step #1006.

In step #1006, it is determined whether or not the shutter releasebutton 111 has been fully depressed (hereinafter described as S2)(S2=ON). If it is determined that it is not S2=ON, then processingreturns to step #1002. By contrast, if it is determined that S2=ON, thenprocessing proceeds to step #1007. It should be noted that, although inthe sequence shown in FIG. 28 processing does not proceed to step #1006if the operations of steps #1003 to #1005 do not end, the presentinvention is not limited to such an arrangement, and thus,alternatively, processing may proceed to step #1006 even if focusing isnot finished. In other words, processing may proceed to exposure byfully depressing the release button even in an out-of-focus state.

In step #1007, it is determined whether or not the camera is in a manualselection mode, in which, depending on the photographer's preference,the splitter 103 is to be positioned in the light path (the effectiveposition shown in FIGS. 26A and 26B) or retracted from the light path.Thereafter, processing proceeds to step #1010 in the selection mode thatenables selection by the photographer or to step #1008 in an automaticselection mode.

When proceeding from step #1007 to step #1008 in the automatic selectionmode, it is determined whether or not to retract the splitter 103 fromthe light path during exposure based on the brightness of the objectimage obtained in step #1001 described above. The splitter 103 itself,as described above, decreases the amount of light that strikes the imagesensing element 106. Therefore, in the case where an object to be sensedis bright which is typical of ordinary image sensing, the splitter 103may be positioned (held) in the light path at the effective positionwithout adverse effect, but in the case where an object to be sensed isdark, the splitter 103 is driven to the retracted position so that anadequate amount of light from the object strikes the image sensingelement 106.

Newer image sensing elements are more sensitive, and therefore there isno need to retract the splitter 103 if the object is slightly dark.Conversely, precisely because the image sensing elements are sosensitive, instances in which the object is so bright that the imagesensing diaphragm must be contracted are increasingly common. In suchcases as these as well, the amount of light can be attenuated by thesplitter 103. Accordingly, there is no need to contract the imagesensing diaphragm, and thus the effects of diffraction and the deepeningof the depth of field that are caused by contracting the diaphragm canbe avoided. Among digital cameras are some types that cope with a brightobject by adjusting the amount of light by inserting an ND filter in thelight path, but for the digital camera according to the presentinvention an ND filter is not needed. Furthermore, because there is noneed to retract the splitter 103 during exposure, the image sensingrelease time lag can be shortened. If the light amount attenuation dueto the holding of the splitter 103 at the effective position is great,the image sensing diaphragm can be expanded or the exposure time can belengthened. Thus, as described above, it becomes possible to carry outimage sensing without retracting the splitter 103 as with ordinary imagesensing, making it possible to smoothly shift from an image sensingpreparatory state to an image sensing state.

By contrast, if the object is extremely dark and the diaphragm iswidened to its maximum extent during image sensing or the exposure timeis lengthened to the point where hand-shake is risked, then the splitter103 is retracted so that an adequate amount of light is directed to theimage sensing element 106 and noise is reduced.

In step #1008 noted above, processing proceeds either to step #1011 ifit is determined that it would be better to retract the splitter 103 tothe retracted position or to step #1009 if the splitter 103 may be leftat the effective position. It should be noted that, in step #1008,specifically the brightness of the object image acquired in step #1001is compared to a preset threshold value, and processing proceeds eitherto step #1009 if the brightness of the object is greater than thethreshold value or to step #1011 if the brightness of the object is lessthan the threshold value. The threshold value is set at the time thecamera is shipped from the factory and is based generally on thesensitivity of the image sensing element 106, the permittivity of thesplitter 103 and so forth. Of course, alternatively, the camera may beconfigured so that the threshold value is changeable according to userpreference.

In step #1009, the exposure operation is carried out in a state in whichthe splitter 103 is positioned at the effective position in the lightpath. The exposure operation resets the charge accumulated in the imagesensing element 106, and, after the lapse of a charge accumulation timethat varies depending on the brightness of the object, shields the imagesensing element 106 from light with a shutter or the like and reads outthe accumulated charge. In addition, the read-out image sensing data issimultaneously recorded on a recording medium at this time. Whenexposure ends, although not shown in this sequence, if the shutterrelease button 111 continues to be pressed (S1, S2=ON), the cameraenters a standby mode in step #1009, during which time the sensed imagecontinues to be displayed on the display device 107. When the shutterrelease button 111 is released, the shutter is once again opened andprocessing returns to step #1002.

In step #1008 described above, when the object is dark and it isdetermined that it would be better that the splitter 103 be retractedduring exposure, processing proceeds to step #1011 as described above,in which it is determined whether the image sensing operation isstill-image image sensing or moving-image image sensing. If the resultsof the determination indicate that the image sensing involvesstill-image image sensing, processing proceeds to step #1012 and thesucceeding processes, in which the splitter 103 is retracted. However,if the results indicate the image sensing involves moving-image imagesensing, then processing proceeds to step #1009 to carry out movingimage recording without retracting the splitter 103. In the latter case,the splitter 103 is not retracted because in the case of moving imagesit is necessary to carry out focus detection and focusing during movingimage recording.

In the case of still-image image sensing, when proceeding from step#1011 to step #1012, the splitter 103 is moved to the retracted positionshown in FIG. 27. Then, in the succeeding step #1013, the plane parallelplate 114 is inserted into the image sensing light flux to compensatefor a change in light path length created by the retraction of thesplitter 103. In the succeeding step #1014 an exposure operation iscarried out as in step #1009. Then, after exposure ends, although notshown in this sequence, if the shutter release button 111 continues tobe pressed (S1, S2=ON), the camera enters a standby mode in step #1014,during which time the sensed image continues to be displayed on thedisplay device 107. When the shutter release button 111 is released, theshutter is once again opened and processing proceeds to step #1015.

In the succeeding step #1015, the splitter 103 is moved to the effectiveposition shown in FIGS. 26A and 26B. Then, in the succeeding step #1016,the plane parallel plate 114 is driven to its original position whichwas inserted to the light path in order to compensate for a change infocus of the image forming optical system 102 caused by the insertion ofthe splitter 103, and processing returns to step #1002.

In addition, where processing proceeds to step #1010 in the selectionmode in which the user selects the position of the splitter 103, it isdetermined if the splitter 103 is selected to be positioned at theeffective position or to be positioned at the retracted position. Wherethe effective position is selected, processing proceeds to step #1009for exposure. By contrast, where the retracted position is selected,processing proceeds to step #1012 and the splitter 103 is retracted.Here, if the retracted position is selected, the camera is constructedso that, in accordance with the user's selection, the splitter 103 ispositioned at the retracted position regardless of whether the image tobe sensed is a still image or a moving image.

Thus, as described above, it is possible to select whether to positionthe splitter 103 in the light path during image sensing or to retract itfrom the light path during image sensing. As a result, even in aninstance in which the object is bright and conventionally the imagesensing diaphragm must be contracted, the attenuation of the amount oflight by the splitter 103 eliminates the need to contract the imagesensing diaphragm, and thus the effects of diffraction and the deepeningof the depth of field that are caused by contracting the diaphragm canbe avoided. In addition, when the object is dark, an adequate amount oflight can still be directed to the image sensing element 106 byretracting the splitter 103.

With the structure described above, the effects of diffraction and thechange in the depth of field that are caused by contracting thediaphragm can be avoided using a simple structure, and can obviate theneed for an ND filter or other such mechanism. Moreover, the releasetime lag during image sensing can also be shortened.

Second Embodiment

FIG. 29 shows a front view of the structure of a light splitting meansincluding the splitter 103 and its holding means installed in a digitalcamera according to a second embodiment of the present invention, inwhich parts having the same functions as in the first embodiment shownin FIGS. 26A and 26B are designated by the same reference numerals. Inaddition, FIG. 30 is a sectional view showing only the significant partsin order to facilitate an understanding of FIG. 29. The rest of thestructure of the digital camera is the same as that of the firstembodiment.

In the second embodiment of the present invention, the structuraldifferences with the first embodiment described above are the followingtwo points: That is, the focus detection sensor 112 is constructed so asto rotate with the splitter 103 as a single unit, and moreover, a focuscorrection transparent panel 207 also rotates as a single unit with thesplitter 103 and is positioned in the light path after retraction of thesplitter 103.

In FIG. 29, the arm 201 that holds the splitter 103 is rotatablysupported with respect to a fixed part of the lens barrel 105 by a shaft205 about which the arm 201 rotates. The rear surface of the splitter103 of the arm 201 is hollowed out, and the image sensing light fluxpasses through the splitter 103 from the object and the image sensinglens and an image is formed on the image sensing element 106. A drivecoil 202 that amounts to a drive motor engages with a gear of the arm201. When an electric current is supplied to the coil 202, the flow ofthe current causes the drive motor to rotate in a direction indicated byarrow 202 k or in the opposite direction thereto. As the drive motorrotates the arm 201 also rotates about the shaft 205 in a directionindicted by arrow 202 l or in the opposite direction thereto.

Stoppers 206 a, 206 b are positioning pins for when the arm 201 comes tothe position shown in FIG. 29. By pressing the arm 201 against thestoppers 206 a, 206 b by an impelling force of the drive coil 202 thepositioning accuracy is increased. In this position (the effectiveposition), the splitter 103 directs the image sensing light flux to boththe focus detection sensor 112 and the image sensing element 106. Thefocus detection sensor 112 also is disposed atop the arm 201 and rotatesas a single unit with the splitter 103 about the shaft 205.

Thus, since the focus detection sensor 112 and the splitter 103 areintegrally formed as a single unit as described above, focus detectionerror due to errors in the relative positions of the focus detectionsensor 112 and the splitter 103 as the splitter 103 is inserted into andretracted from the light path can be eliminated.

In FIG. 30, the splitter 103 is fixed on the arm 201. Similarly thefocus detection sensor 112 is also fixed on the arm 201. A light fluxtraveling along the optical axis 104 is directed not only to the imagesensing element 106 but also to the focus detection sensor 112 by beingreflected by two light-splitting surfaces inside the splitter 103 and atotal reflection surface disposed therebetween. The arm 201 rotatesabout the shaft 205 so as to enable the exchange of the splitter 103 andthe transparent panel 207 within the light path. When the splitter 103is positioned at the retraction position and an electric current isapplied to the drive coil 202, the arm 201 is subjected to a forceexerted in the direction indicated by arrow 202 l. As a result, the arm201 starts to rotate clockwise about the shaft 205 and the splitter 103is positioned at the retraction position.

FIG. 31 is a flow chart illustrating the operation of the mechanismshown in FIGS. 29 and 30 through an image sensing sequence of a camera.This sequence of operations starts when the camera power is turned onand ends when the power is turned off. It should be noted that, to avoidcomplication, descriptions of the operations of elements not directlyrelated to the present invention and the detailed operation of each step(for example, confirmation after an operation or a standby operationwith a timer) are omitted.

In step #1001, the image sensing element 106 is driven, object imageinformation is collected, a variety of processes are carried out on theobject image information with the RGB image processing circuit 131 andthe YC processing circuit 132, and the processed object imageinformation is output to the display device 107 so that the object imagecan be checked on the display device 107. In addition, during thisseries of processes the brightness of the object is obtained, anddepending on that brightness, the diaphragm inside the lens barrel 105is adjusted and signals output from the image sensing element 106 areboosted so as to enable an object image of appropriate brightness to bedisplayed on the display device 107. Furthermore, this brightnessinformation is used in step #1008 to determine the necessity ofretracting the splitter 103.

Next, in step #1002, the cycling of step #1001 continues in a standbymode until the shutter release button 111 is pressed halfway and S1=ON.Thereafter, when S1=ON, processing proceeds to step #1003. Then, in step#1003, charge corresponding to a light flux striking the focus detectionsensor 112 through the splitter 103 is accumulated and detection of thedefocus amount (detection of the focus state) is carried out. Thus, thesplitter 103 normally is positioned within the optical path of the imagesensing lens (the effective position shown in FIG. 29).

Next, in step #1004, in accordance with the focus detection results,part or all of the image forming optical system 102 is driven and theobject image is focused on the surface of the image sensing element 106.Then, in the next step #1005, charge corresponding to the light fluxstriking the focus detection sensor 112 is again accumulated and thedefocus amount is detected to confirm that the image is in focus.Although omitted from this sequence, if it is determined here that thefocus is inadequate, then, based on that result, the image formingoptical system 102 is again driven to correct the focus and the focusconfirmation operation is repeated. If after multiple iterations of theoperations described above the image is still out of focus, then amessage indicating that the camera cannot focus is displayed, focusingis stopped and processing proceeds to step #1006.

In step #1006, it is determined whether or not the shutter releasebutton 111 has been fully depressed and S2=ON. If it is determined thatit is not S2=ON, then processing returns to step #1002. By contrast, ifit is determined that S2=ON, then processing proceeds to step #1007. Itshould be noted that, although in the sequence shown in FIG. 31processing does not proceed to step #1006 if the operations of steps#1003 to #1005 do not end, the present invention is not limited to suchan arrangement, and thus, alternatively, processing may proceed to step#1006 even if focusing is not finished. In other words, processing mayproceed to exposure by fully depressing the release button even in anout-of-focus state.

In step #1007, it is determined whether or not the camera is in a manualselection mode, in which, depending on the photographer's preference,the splitter 103 is to be positioned in the light path (the effectiveposition shown in FIG. 29) or retracted from the light path. Thereafter,processing proceeds to step #1010 in the selection mode that enablesselection by the photographer or to step #1008 in an automatic selectionmode.

When proceeding from step #1007 to step #1008 in the automatic selectionmode, it is determined whether or not to retract the splitter 103 fromthe light path during exposure based on the brightness of the objectimage obtained in step #1001 described above. The splitter 103 itself,as described above, decreases the amount of light that strikes the imagesensing element 106. Therefore, in the case where an object to be sensedis bright which is typical of ordinary image sensing, the splitter 103may be held in the light path at the effective position without adverseeffect, but in the case where an object to be sensed is dark thesplitter 103 is driven to the retracted position so that an adequateamount of light from the object strikes the image sensing element 106.

In step #1008 noted above, processing proceeds either to step #1012 ifit is determined that it would be better to retract the splitter 103 tothe retracted position or to step #1009 if the splitter 103 may be leftat the effective position. In step #1009, the exposure operation iscarried out in a state in which the splitter 103 is positioned at theeffective position in the light path. The exposure operation resets thecharge accumulated in the image sensing element 106, and, after thelapse of a charge accumulation time that varies depending on thebrightness of the object, shield the image sensing element 106 fromlight with a shutter or the like and reads out the accumulated charge.In addition, the read-out image sensing data is simultaneously recordedon a recording medium at this time. When exposure ends, although notshown in this sequence, if the shutter release button 111 continues tobe pressed (S1, S2=ON), the camera enters a standby mode in step #1009,during which time the sensed image continues to be displayed on thedisplay device 107. When the shutter release button 111 is released, theshutter is once again opened and processing returns to step #1002.

In step #1008 described above, when the object is dark and it isdetermined that it would be better that the splitter 103 be retractedduring exposure, processing proceeds to step #1012 as described aboveand the splitter 103 is moved to the retracted position.

It should be noted that, in the first embodiment of the presentinvention as described above, in step #1011 shown in FIG. 28 it isdetermined if image sensing is still image sensing or moving imagesensing and the splitter 103 is fixed at the effective position even ifthe object is dark in the case of moving image sensing. By contrast, inthe second embodiment of the present invention, step #1011 is omitted,and thus, if the object is dark, the splitter 103 is retracted even inthe case of moving image sensing so that an adequate amount of light canbe obtained at the image sensing element 106. In that case, the focusdetection using the focus detection sensor 112 cannot be conductedduring moving image sensing. Of course, focusing is carried out fromsteps #1003 to #1005, and thus the object image is in focus at the startof moving image recording, but if the object image moves during movingimage sensing or the photographer pans the camera, focus detectioncannot be repeated.

However, the image sensing light flux is directed to the image sensingelement 106 during moving image sensing, and therefore, based on thatinformation, it is possible to continue focusing using the contrast ofthe object image (so-called TV-AF operation). In other words, if theobject is dark, the splitter 103 is retracted even in the case of movingimage recording so as to increase the amount of light striking the imagesensing element 106 and to prevent the occurrence of noise. Accordingly,changes in focus may be detected using the signals output from the imagesensing element 106 and the image forming optical system 102 maycontinue to be driven.

In addition, in the first embodiment described above, from step #1012 tostep #1013 shown in FIG. 28, an optical member for correcting the lightpath length (the plane parallel plate 114) is inserted into the imagesensing light flux (or, alternatively, the image forming optical system102 may be driven along the optical axis) to compensate for the changein light path length brought about by the retraction of the splitter103. By contrast, in the second embodiment, those steps are omittedbecause focus change compensation can be carried out by inserting thetransparent panel 207 having the same thickness as the splitter 103 intothe light path in place of the splitter 103.

In the succeeding step #1014 an exposure operation is carried out as instep #1009. Then, after exposure ends, although not shown in thissequence, if the shutter release button 111 continues to be pressed (S1,S2=ON), the camera enters a standby mode in step #1014, during whichtime the sensed image continues to be displayed on the display device107. When the shutter release button 111 is released, the shutter isonce again opened and processing proceeds to step #1015.

Next, in step #1015, the splitter 103 is moved to the effective positionshown in FIG. 29 and processing returns to step #1002.

In addition, where processing proceeds to step #1010 in the selectionmode in which the user selects the position of the splitter 103, it isdetermined if the splitter 103 is selected to be positioned at theeffective position or to be positioned at the retracted position. Whereeffective position is selected, processing proceeds to step #1009 forexposure. By contrast, where the retracted position is selected,processing proceeds to step #1012 and the splitter 103 is retracted.Here, if it the retracted position is selected, the camera isconstructed so that, in accordance with the user's selection, thesplitter 103 is positioned at the retracted position regardless ofwhether the image is a still image or a moving image.

Thus, as described above, it is possible to select whether to positionthe splitter 103 in the light path during image sensing or to retract itfrom the light path during image sensing. As a result, even in aninstance in which the object is bright and conventionally the imagesensing diaphragm must be contracted, the attenuation of the amount oflight by the splitter 103 eliminates the need to contract the imagesensing diaphragm, and thus the effects of diffraction and the deepeningof the depth of field that are caused by contracting the diaphragm canbe avoided. In addition, if the object is dark, an adequate amount oflight can still be directed to the image sensing element 106 byretracting the splitter 103.

With the structure described above, the effects of diffraction and thedeepening of the depth of field that are caused by contracting thediaphragm can be avoided using a simple structure, and can obviate theneed for an ND filter or other such mechanism. Moreover, the releasetime lag during image sensing can also be shortened. Furthermore, sincethe focus detection sensor 112 and the splitter 103 are integrated as asingle unit, focus detection error due to errors in the relativepositions of the focus detection sensor 112 and the splitter 103 as thesplitter 103 is driven to the effective position and the retractedposition can be eliminated.

Third Embodiment

FIG. 32 is a flow chart illustrating the operation of the main parts ofa digital camera according to a third embodiment of the presentinvention. This sequence of operations starts when the camera power isturned on and ends when the power is turned off. It should be notedthat, to avoid complication, descriptions of the operations of elementsnot directly related to the present invention and the detailed operationof each step (for example, confirmation after an operation or a standbyoperation with a timer) are omitted. In addition, the structures of thedigital camera of the third embodiment are the same as those of thefirst or second embodiments described above.

In step #1001, the image sensing element 106 is driven, object imageinformation is collected, a variety of processes are carried out on theobject image information with the RGB image processing circuit 131 andthe YC processing circuit 132, and the processed object imageinformation is output to the display device 107 so that the object imagecan be checked on the display device 107. In addition, during thisseries of processes the brightness of the object image is obtained, anddepending on that brightness, the diaphragm inside the lens barrel 105is adjusted and signals output from the image sensing element 106 areboosted so as to enable an object image of appropriate brightness to bedisplayed on the display device 107. Furthermore, this brightnessinformation is used in step #1008 to determine the necessity ofretracting the splitter 103.

Next, in step #1002, the cycling of step #1001 continues in a standbymode until the shutter release button 111 is pressed halfway and S1=ON,after which, when S1=ON, processing proceeds to step #1003. Then, instep #1003, charge corresponding to a light flux striking the focusdetection sensor 112 through the splitter 103 is accumulated anddetection of the defocus amount (detection of the focus state) iscarried out. Thus, the splitter 103 normally is positioned within theoptical path of the image sensing lens (the effective position shown inFIGS. 26A and 26B or FIG. 29).

Next, in step #1004, in accordance with the focus detection results,part or all of the image forming optical system 102 is driven and theobject image is focused on the surface of the image sensing element 106.Then, in the next step #1005, charge corresponding to the light fluxstriking the focus detection sensor 112 is again accumulated and thedefocus amount is detected to confirm that the image is in focus.Although omitted from this sequence, if it is determined here that thefocus is inadequate, then, based on that result, the image formingoptical system 102 is again driven to correct the focus and the focusconfirmation operation is repeated. If after multiple iterations of theoperations described above the image is still out of focus, then amessage indicating that the camera cannot focus is displayed, focusingoperation is stopped and processing proceeds to step #1006.

In step #1006, it is determined whether or not the shutter releasebutton 111 has been fully depressed and S2=ON. If it is determined thatit is not S2=ON, then processing returns to step #1002. By contrast, ifit is determined that S2=ON, then processing proceeds to step #1011. Itshould be noted that, although in the sequence shown in FIG. 32processing does not proceed to step #1006 if the operations of steps#1003 to #1005 do not end, the present invention is not limited to suchan arrangement, and thus, alternatively, processing may proceed to step#1006 even if focusing is not finished. In other words, processing mayproceed to exposure by fully depressing the release button even in anout-of-focus state.

In step #1011, it is determined if the exposure mode involves movingimage sensing or still image sensing, and processing proceeds either tostep #1008 for moving image sensing or to step #1012 for still imagesensing.

Proceeding to step #1008, photometry results obtained in step #1001 areexamined. As a result, if the object is bright then processing proceedsto step #1009, and exposure is carried out with the splitter 103 beingpositioned at the effective position in the light path. The exposureoperation resets the charge accumulated in the image sensing element106, and, after the lapse of a charge accumulation time that variesdepending on the brightness of the object image, shield the imagesensing element 106 from light with a shutter or the like and reads outthe accumulated charge. In addition, the read-out image sensing data issimultaneously recorded on a recording medium at this time. Whenexposure ends, although not shown in this sequence, if the shutterrelease button 111 continues to be pressed (S1, S2=ON), the cameraenters a standby mode in step #1009, during which time the sensed imagecontinues to be displayed on the display device 107. When the shutterrelease button 111 is released, the shutter is once again opened andprocessing returns to step #1002.

In step #1008 described above, when the object is dark and it isdetermined that it would be better that the splitter 103 be retractedduring exposure, processing proceeds to step #1012 as described aboveand the splitter 103 is moved to the retracted position. Then, in thesucceeding step #1014, an exposure operation is carried out as in step#1009. Then, after exposure ends, although not shown in this sequence,if the shutter release button 111 continues to be pressed (S1, S2=ON),the camera enters a standby mode in step #1014, during which time thesensed image continues to be displayed on the display device 107. Whenthe shutter release button 111 is released, the shutter is once againopened and processing proceeds to step #1015.

Next, in step #1015, the splitter 103 is moved to the effective positionand processing returns to step #1002.

Thus, as described above, in moving image sensing the splitter 103 canbe held at either the effective position or the retracted positiondepending on image sensing conditions, and in still image sensing thesplitter 103 is positioned at the retracted position during imagesensing. As a result, with moving image sensing, even if the object isbright and the image sensing diaphragm must be contracted, theattenuation of the amount of light by the splitter 103 eliminates theneed to contract the image sensing diaphragm, and thus the effects ofdiffraction and the deepening of the depth of field that are caused bycontracting the diaphragm can be avoided. In addition, if the object isdark, an adequate amount of light can be directed to the image sensingelement 106 by retracting the splitter 103. Moreover, with still imagesensing, an adequate amount of light can still be directed to the imagesensing element 106.

In other words, when the object in moving image sensing is bright,nimble focusing is possible using the focus detection sensor 112, andwhen the object is dark an adequate amount of light can still beprovided to the image sensing element 106.

Although in the foregoing embodiments the description proceeds using adigital camera as an example, it should be noted that the presentinvention is not limited to a digital camera and can also be adapted toa video camera, a surveillance camera, a Webcam, a mobile phone equippedwith an image sensing capability or the like.

The present invention is not limited to the above embodiments, andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore, to apprise the public of thescope of the present invention, the following claims are made.

This application claims the benefit of Japanese Patent Application No.2005-113345 filed on Apr. 11, 2005, which is hereby incorporated byreference herein in its entirety.

1. An image sensing apparatus comprising: a light flux splitter disposedbetween a lens that focuses light flux of an object image on an imagesensing surface and that image sensing surface and that branches thelight flux of the object image out of an image sensing light path; alight receiving unit that receives the light flux of the object imagebranched by said light flux splitter and obtains a signal for focusingcontrol of the lens; and a holding unit that holds said light fluxsplitter at either an effective position within the image sensing lightpath or at a retracted position outside the image sensing light path,wherein the image sensing apparatus automatically holds said light fluxsplitter at either the effective position or the retracted positiondepending on image sensing conditions.
 2. The image sensing apparatusaccording to claim 1, wherein said holding unit holds said light fluxsplitter at either the effective position or the retracted positionduring image sensing in response to a user selection operation.
 3. Theimage sensing apparatus according to claim 1, further comprising aphotometry unit that measures a brightness of an object image, whereinsaid holding unit automatically holds said light flux splitter at eitherthe effective position or the retracted position depending on thebrightness measured by said photometry unit.
 4. The image sensingapparatus according to claim 3, wherein said holding unit holds saidlight flux splitter at the effective position during image sensing inresponse to moving image sensing being selected.
 5. The image sensingapparatus according to claim 3, wherein said holding unit holds saidlight flux splitter at the effective position during image sensing ifthe brightness of the object image is greater than a preset thresholdvalue.
 6. The image sensing apparatus according to claim 3, wherein saidholding unit holds said light flux splitter at the effective positionduring image sensing if the brightness of the object image is greaterthan a preset threshold value, and further, moving image sensing isselected.
 7. The image sensing apparatus according to claim 1, wherein,when said holding means holds said light flux splitter at the retractedposition during image sensing, an optical member for compensating thechange in light path length caused by retraction of said light fluxsplitter from the effective position is inserted into the image sensinglight path.
 8. The image sensing apparatus according to claim 1,wherein, when said holding means holds said light flux splitter at theretracted position during image sensing, the lens is moved along theoptical axis by an amount that compensates the change in a light pathlength caused by retraction of said light flux splitter from theeffective position.
 9. The image sensing apparatus according to claim 1,wherein said holding unit moves said light flux splitter to theretracted position after image sensing is instructed.
 10. A controlmethod for an image sensing apparatus having a light flux splitterdisposed between a lens that focuses light flux of an object image on animage sensing surface and that image sensing surface and that branchesthe light flux of an object image out of an image sensing light path, alight receiving unit that receives the light flux of the object imagebranched by the light flux splitter and obtains a signal for focusingcontrol of the lens; and a holding unit that holds the light fluxsplitter at either an effective position within the image sensing lightpath or at a retracted position outside the image sensing light path,the control method comprising: determining whether to carry out imagesensing with the light flux splitter at the effective position or at theretracted position depending on image sensing conditions; and retractingthe light flux splitter to the retracted position prior to image sensingif it is determined that image sensing is to be carried out with thelight flux splitter positioned at the retracted position.